(1) Field of the Invention
The present invention relates to temperature measurement and particularly to the measurement of small differential temperatures between widely-spaced points. More specifically, this invention is directed to a system for simultaneously measuring both differential and absolute temperatures. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While limited thereto in its utility, the present invention is particularly well suited for providing accurate information from which the atmospheric "lapse rate", or vertical temperature gradient, can be computed. For this purpose, the difference in temperature between two points vertically separated by, for example, 100 feet is measured. This temperature differential, which is generally quite small--i.e., on the order of tenths of a C.degree.--may be of interest for several reasons. By way of example only, the strength and decay rate of the wake vortices produced by a fixed-wing aircraft during landing or take off will be affected by the temperature "lapse rate". Knowledge of wake-vortex strength and position is of interest to flight controllers since the separation which must be maintained between landing and departing aircraft is a function of this information.
In a typical wake-vortex monitoring system, a pair of temperature sensors will be positioned on towers at points vertically separated by 50 to 150 feet and the difference in temperature between the two separated points will be continuously monitored. As noted above, this atmospheric temperature difference is minute. Accordingly, in order to obtain accurate "lapse rate" information, the "equivalent temperature" errors introduced by the measuring system must be made extremely small so as to have a negligible effect. Additionally, the accuracy of the measurement system must be maintained over a wide range of atmospheric temperatures such as, for example, from -30.degree. C. to +50.degree. C.
Previously proposed atmospheric-temperature-gradient measuring systems have been plagued by inaccuracies arising from such factors as amplifier offset and drift, differences in signal attentuation between the spaced sensors, and other errors introduced by the differential-temperature-computation circuitry. Accordingly, it has not been previously possible to accurately and reliably measure minute atmospheric temperature gradients for demanding applications such as aircraft wake-vortex monitors.